In general, permanent waving of human hair is achieved by chemically breaking the sulfur to sulfur or disulfide cystine bonds occurring naturally in human hair and then reforming the cystine bonds while the hair is wrapped or curled on rods. The sulfur to sulfur cystine bonds in human hair maintain the hair in a naturally straight or curly configuration and, in order to permanently reshape the hair into a lasting, different configuration, a significant percentage of the sulfur to sulfur bonds must be broken and then reestablished after the hair is reconfigured in a desired position, such as wrapped around a suitable mandrel or roller. In general, the sulfur to sulfur cystine bonds are broken with a composition containing a reducing agent and after the hair is wound into a curl formation around a rod or roller, the sulfur to sulfur cystine bonds are relinked or reestablished while the hair is in the curl formation by contacting the hair in the new formation with an oxidizing agent, such as hydrogen peroxide or a water-soluble bromate.
There are three general types of permanent wave compositions or lotions used to break the cystine bonds in human hair, generally known as acid wave compositions; alkaline wave compositions; and neutral wave compositions. Of these three, the acid and alkaline wave compositions are most significant commercially. Permanent wave compositions containing an alkaline salt of thioglycolic acid (TG), such as ammonium thioglycolate as the reducing agent, are generally known as alkaline wave compositions and generally have a pH in the range of about 7.5 to about 9.4. The alkaline wave compositions are known as the conventional cold wave compositions, since free alkali penetrates and swells the hair shaft allowing the reducing agent to enter the hair shaft and break the sulfur to sulfur bonds without added heat. The permanent wave compositions containing glycerol monothioglycolate (GMTG) are known as acid wave compositions even though the pH of these compositions can be as high as about 9.0. Generally speaking, the acid permanent wave compositions have a lower pH than the alkaline permanent wave compositions and, therefore, require heat and/or longer processing time to achieve sufficient reaction of the reducing agent. The alkaline permanent wave compositions produce a stronger, longer lasting curl while the acid permanent wave compositions provide a softer feel but a shorter curl duration. The permanent wave compositions containing an alkaline salt of thioglycolic acid and/or glycerol monothioglycolate leave the hair with a very noticeable sulfur odor.
The reducing action of mercaptans on keratin is due mostly to the dissociated form of the thiol groups, the thiolate anion. Acid permanent waves sufficiently curl hair at a lower pH compared to alkaline permanents because the waving agents in these permanents have low pKa values and thus exist predominantly in dissociated (thiolate) form at a pH near neutral, or slightly acidic pH. Hence, the pKa value shows that some mercaptans are efficient at high pH while others with a low pKa value and high ionization constant are efficient at lower pH values. For example, it is well known that the alkaline salts of thioglycolic acid, e.g., the ammonium salt of thioglycolic acid (pKa=10.4) has acceptable waving efficiency only if the pH of solution exceeds 9.0, see Zviak, Charles, The Science of Hair Care, Permanent Waving and Hair Straightening, p. 191, 1986; while amides such as thioglycolamide (pKa=8.4), and esters such as glycerol thioglycolate (pKa=7.8) give acceptable waving efficiency at neutral and even slightly acid pH.
The cysteine and thioglycolate-based reducing agent-containing composition and method of the present invention are unexpectedly effective in the pH range of about 7.5 to about 9.5 and particularly in the pH range of about 9.0 to about 9.5. Compositions having a pH in the lower end of the pH range (e.g., about 7.5 to about 8.5) are most effective for bleached hair, while compositions having a pH in the higher end (e.g., about 9.0 to about 9.5) are most effective for normal and curl-resistant hair. A number of compositions can be provided that are particularly suited for permanent waving hair in different conditions.
For example, a composition for permanently waving normal and tinted hair (hair with little damage) contains about 5.0% to about 7.0% thioglycolate and about 4.0% to about 6.0% cysteine; a composition for bleached hair contains about 3.5% to about 5.5% thioglycolate and about 2.0% to about 4.0% cysteine; and a composition for curl-resistant hair contains about 5.5% to about 7.5% thioglycolate and about 5.0% to about 6.5% cysteine.
Different reducing agents are effective to break the cystine bonds that cross link human hair protein at different pH's. Generally speaking, the acid permanent wave compositions having a lower pH include reducing agents such as bisulfites, e.g., ammonium bisulfite, or glycerol monothioglycolate, capable of breaking the sulfur to sulfur cystine bonds within lower pH ranges, whereas the alkaline permanent wave compositions, having pH's in the range of about 7.5 to 9.5, require an alkaline salt of thioglycolic acid or an alkaline salt of a dithioglycolic acid--so that the alkali can penetrate and swell the hair shaft for easier penetration of the reducing agent in order to break the sulfur to sulfur cystine bonds.
Perhaps the most difficult factor for the applier of the permanent wave lotion to assess in determining how long to apply the reducing agent to the hair is the condition of the hair at the time of the permanent wave. It is well documented in the literature and prior art that the hair can be damaged by abuse of chemicals, e.g., by shampooing, permanent waving, tinting, frosting, bleaching, and particularly any hair treatment involving the use of hydrogen peroxide; mechanical treatment, e.g., thermal appliances; and environmental conditions, e.g., climate and pollution. It is well known that damaged hair, depending upon the stage and degree of damage of the hair, has significantly different chemical activity to reducing agents than normal or undamaged hair. If too many of the sulfur to sulfur bonds in the hair are broken by the reducing agent, the hair will be seriously weakened and may disintegrate.
It is theorized that somewhere in the range of about 20% to about 60% of the natural sulfur to sulfur cystine bonds in the hair shafts should be broken in order to give the hair the capability of being reshaped to any desired shape, such as curled around a rod or roller, and capable of retaining this shape. If too few of the sulfur to sulfur bonds are broken, the natural or normal configuration of the hair will predominate, causing the hair to retain its previous shape. This is because the predominant prior or natural bonds in the hair dictate that the hair will remain in the old configuration or shape. Hydrogen bonds are physically broken when wet hair is stretched and wrapped around a roller. When the hair is dried, the hydrogen bonds are reformed in a curled position or shape. While the hydrogen bonds aid to maintain the hair in the new configuration, the sulfur to sulfur cystine bonds are much stronger and, to a much greater extent than the hydrogen bonds, control the efficacy of the permanent wave.
In order to successfully provide a satisfactory permanent wave in the hair, the sulfur to sulfur cystine bonds reformed in the hair in the new or curled configuration, when the hair is later oxidized with the neutralizing agent, should be as strong as the prior or natural cystine hair bonds. It is desired, therefore, when permanent waving, that enough new bonds in a new hair configuration are formed during permanent waving to equal the number of old bonds remaining that tend to form the hair in its prior or natural configuration, whether it be straight or naturally curled.
Generally, the reducing agent lotion is applied to the hair by first shampooing the hair and then applying the reducing agent lotion to the hair, either before or after the hair is wrapped around suitable rollers. When the reducing agent lotion is applied to sections of the head prior to rolling that portion of the hair onto the rods it is called a lotion wrap whereas when the hair is rolled on the rods or rollers first and then the lotion applied onto all of the hair after rolling, this is called a water wrap. The timing for the reducing agent to be in contact with the hair for a lotion wrap is begun from the time that all rods are on the head, and the timing for a water wrap begins from the time that the lotion application is completed. The capability of using a water wrap is clearly more desirable since the lotion is applied to the entire head of hair all at once in a short period of time and can be rinsed from the hair all at once to provide a more uniform reducing agent contact time for all of the hair.
In accordance with the present invention, an alkaline permanent wave composition is provided in a single formula capable of being water wrapped with or without the use of a dryer, heating caps or other heat treatment to speed the reducing agent reaction. The composition of the present invention produces a strong curl similar to alkaline wave composition yet leaves the hair feeling soft like an acid wave composition without post-perm odor normally associated with thioglycolate-containing, e.g., ammonium thioglycolate-containing permanent wave composition.
Prior art alkaline compositions containing a salt of thioglycolic acid as a reducing agent are known to produce a tight curl but leave the hair feeling harsh due to the high alkalinity content. Such compositions, however, produce a distinct post-perm sulfur odor, even if used with cysteine, due to the presence of too high a concentration of ammonium thioglycolate; or such compositions have a low perm efficacy. Prior art acid wave compositions containing glycerol monothioglycolate also leave the hair with a strong sulfur odor. Acid wave compositions generally require heat to help swell the hair for reaction with the reducing agent since the hair is not normally swelled sufficiently at the low pH of the acid wave compositions. The cysteine, thioglycolate-based reducing agent-containing permanent wave compositions of the present invention solve the above mentioned prior art deficiencies without causing a post-perm odor, even immediately after the permanent wave composition is applied.